Tetramethylammonium hydroxide (TMAH) is used as an etchant of silicon. When etching trenches in silicon using TMAH, hillocks are formed on the bottom and sides of the trench. FIGS. 1A and 1B illustrate such hillocks.
As shown in FIG. 1A, which is a cross-sectional view, an apparatus 100 includes a trench 102 formed in silicon 104. The trench is etched in the silicon using TMAH, and includes a bottom surface 106 and sidewalls 108. As a result of using TMAH as the etchant, hillocks 110 are formed. The hillocks are characterized by a pyramidal shape, are typically densely formed, and are of various sizes.
FIG. 1B is an image taken of a trench in silicon formed using conventional TMAH etch techniques. The top down view looks down on the bottom 106 of a trench having sidewalls 108. The hillocks 110 are visible on the bottom surface of the trench.